In the semiconductor industry the fabrication of microelectronic circuits typically uses single-crystal silicon and typically requires that several thin films of both insulating and conducting materials be formed and patterned sequentially on the silicon surface. The conventional wiring above a semiconductor substrate utilizes aluminum conductors with a small amount of copper, however, some microcircuits have been proposed using copper conductors. Copper wiring and electroless copper eposition are, of course, known for printed circuit boards.
Generally, the insulating films are a dense silicon dioxide dielectric, both horizontally between the conductors (intralevel dielectric) and vertically between layers of conductors (interlevel dielectric). Metal filled vias are used, e.g., to provide electrical connections between conductors in different levels. Such metal filling has generally been provided by physical vapor deposition (PVD), e.g. sputtering or vacuum deposition.